1. Field of the Invention
The invention relates to a method according to the preamble of claim 1 for selecting the frequency range in radio communication devices operating in several frequency ranges, so called multiband radio communication devices.
The invention also relates to a multiband radio communication device.
2. Description of the Prior Art
Of the existing digital cellular networks, the GSM (Global System for Mobile telecommunications) is the most extensively used at the moment. Because the networks suffer from congestion, the GSM system, which originally had an operating frequency of 900 MHz, has been extended to 1.8 GHz. There are also cellular networks of other standards widely used in the world. Because the mobility of people and communications between people are increasing, there is a need for combined telephones, which operate on several different networks, depending on which network is available and/or which network offers services to the users at the lowest price.
In addition, in the so called third generation cellular systems (UMTS/FLPMTS, Universal Mobile Telecommunication System/Future Public Land Mobile Telecommunication System) it is possible to use several frequency ranges within the same system. Because of these reasons, efforts have been made to develop radio communication devices which can operate in several different frequency ranges and/or in network systems of different standards. In order to simplify the explanation, the frequency ranges used by different systems are handled in this patent application as if they were always different frequency ranges, although in some cases it is possible that different systems use the same frequency ranges.
In radio communication devices operating in many different frequency ranges, the duplexing and multiple access methods of different systems must be matched. Duplexing means separating communications in the transmit and receive direction from each other in a data transfer connection between two transceiver devices. Common methods are Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). Multiple access means dividing the capacity of the system or a part of it (such as a base station) between many terminal devices (such as radio communication devices). Common methods are Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA). In addition, different multiplexing methods are applied in the systems, whereby one device directs information received from several sources to a common transfer channel and separates the transmissions from one another e.g. by Time Division Multiplexing (TDM) or Frequency Division Multiplexing (FDM), for example.
A prior art radio communication device operating in two directions by time or frequency division multiplexing contains many RF and intermediate frequency filters both on the transmit (TX) and receive (RX) side. FIG. 1 shows a prior art GSM communication device 100. In the GSM system, the transmission and reception take place in different time slots and at different frequencies. The communication device 100 includes the receiver (RX) branch 11 and the transmitter (TX) branch 12. The selection of whether the communication device operates in the reception state or the transmission state can be performed by means of an antenna switch (not shown) placed e.g. between the inputs of the branches 11 and 12 and the antenna 21, whereby the selected branch is connected to the antenna 21. The antenna switch that connects the antenna to the transmitter branch 11 and the receiver branch 12 in turn, is used in radio communication devices for separating the signals if the system has time division duplexing (TDD). If the transmission and reception take place in different frequency ranges, a filter 22 like the duplex filter used in analog telephones can be used as the separating unit, as in the solution shown in FIG. 1.
The duplex filter 22 is a circuit device with three gates, comprising a reception branch filter 22RX between the antenna and reception gate and a transmission branch filter 22TX between the transmitter and antenna gate. The operating frequencies of the filters have been selected so that a transmission frequency signal does not get to the receiver gate and a reception frequency signal does not get to the transmission gate. The frequency properties of the filters can be adjustable.
On the reception side 11, the GSM communication device 100 includes a Low Noise Amplifier (LNA) 32, the input gate of which is connected to the duplex filter 22. The amplifier 32 is followed by a bandpass filter 33, which filters the received signal. The output gate of the filter 33 is connected to a mixer 34, in which the received signal is mixed with the first mixing signal coming from the synthesizer 23. The intermediate frequency signal produced as the mixing result is directed to the RF circuit 35 of the receiver for further processing.
The signal 45 produced in the transmitter part 12 of the communication device 100 at the pre-stage of the transmitter (not shown) is mixed in the mixer 44 with the first mixing signal. The output of the mixer 44 is taken to the bandpass filter 43, which is generally situated before the power amplifier 42 of the transmitter. The output of the power amplifier 42 is coupled through the duplex filter 22 to the antenna 21. Between the power amplifier 42 and the duplex filter 22 there is often a directional coupler (not shown), by which the power level of the signal going to the antenna can be measured.
FIG. 2 shows a prior art dual mode radio communication device 200 operating in two different frequency ranges as an example of multiband radio communication devices operating in several frequency ranges. In the radio communication device 200, both frequency ranges share the same antenna 21. An antenna switch 50 connects the shared antenna 21 to the component chain (a or b) forming the desired transmitter-receiver according to the frequency range used. The operations of the selected component chain are mainly the same as shown in FIG. 1 and in the case of the component chain a they comprise a duplex filter 22a and in the reception branch RXa an amplifier 32a and a bandpass filter 33a, and in the transmission branch TXa a bandpass filter 43a and a power amplifier 42a. Correspondingly, when another frequency range/system is used, the components being used are the duplex filter 22b and the signal path going through the amplifier 32b of the reception branch RXb and the filter 33b, or the signal path going through the filter 43b of the transmitter branch TXb and the amplifier 42b. 
Switch 51 on the reception side and switch 52 on the transmission side operate synchronously with the antenna switch 50 and connect the selected transmission and reception branches via mixers 34 and 44 to the common modulation and demodulation components of a dual mode telephone, and through them to other components of the communication device.
The prior art solution shown in FIG. 2 above has the problem of attenuation in the switches 50, 51, 52 and in the duplex filters 22a and 22b. 
An object of the invention is to provide a new method for selecting the frequency range of a radio communication device that operates i.e. transmits and/or receives in at least two different frequency ranges.
Another object of the invention is to provide a new radio communication device, especially a new mobile station.
A method according to the invention for selecting one of the frequency ranges of a radio communication device operating in at least two different frequency ranges, comprises the step of activating an amplifier in a signal path corresponding to said frequency range among the group of the amplifiers placed in the signal paths of a signal branch of the radio communication device. In a preferred embodiment of the invention the activating of said amplifier is produced by switching on the amplifier.
Another method according to the invention for selecting the frequency range of a radio communication device such as a radio transceiver transmitting and receiving in at least two different frequency ranges, comprises the step of activating the first amplifier among the first group of the amplifiers placed in the reception branch of the radio communication device which first amplifier is located in a signal path corresponding to said frequency range and activating the second amplifiers among the second group of the amplifiers placed transmission branch of the radio communication device which second amplifier is located in a signal path corresponding to said frequency range. In a preferred embodiment of the invention the activating of said first and second amplifiers is produced by switching on the amplifiers.
Another advantageous method according to the invention for selecting the frequency range of a radio communication device operating in at least two different frequency ranges, comprises the step of directing an input signal in a signal branch containing the desired information to the first group of bandpass filters, separating each frequency range to its own signal path by means of the first group of bandpass filters, selecting the desired frequency range and the signal path by activating an amplifier among the group of amplifiers arranged in the signal paths after the first group of bandpass filters which amplifier corresponds to the desired frequency range, directing the signals of different signal paths received from the group of amplifiers to the second group of bandpass filters, and recombining the signals from different signal paths after the second group of bandpass filters into an output signal.
A radio communication device according to the invention operating at least two different frequency ranges comprises a group of the amplifiers placed in a signal branch of the radio communication device, and a selecting means for selecting one of the frequency ranges having an activating means for activating an amplifier among said group of the amplifiers in a signal path of the signal branch corresponding to said frequency range. In a preferred embodiment the activating means comprises an actuator unit for switching on and off said amplifier.
Another radio communication device according to the invention operating at least two different frequency ranges comprises successively in a signal branch of the device: a first group of bandpass filters; a group of the amplifiers; and a second group of bandpass filters; which filters in the first and second group of filters and the amplifiers are arranged so that parallel signal paths for each frequency ranges are defined, which device further comprises a selecting means for selecting one of the frequency ranges having an activating means for activating an amplifier among said group of the amplifiers in the signal path corresponding to said frequency range.
Another advantageous radio communication device such as a radio transceiver according to the invention operating at least two different frequency ranges having a reception branch for receiving radio signals in one of the frequency ranges and a transmission branch for transmitting radio signals in the same frequency range as receiving radio signals which device comprises in the reception branch; a first group of bandpass filters; a first group of amplifiers; and a second group of bandpass filters which device further comprises in the transmission branch; a third group of bandpass filters; a second group of amplifiers; and a fourth group of bandpass filters; which filters in the first and second group of filters and the first group of amplifiers are arranged so that parallel signal paths for each frequency ranges are defined, and which filters in the third and fourth group of filters and the second group of amplifiers are arranged so that parallel signal paths for each frequency ranges are defined, which device further comprises a selecting means for selecting one of the frequency ranges having an activating means for activating an amplifier in the reception and transmission branch among said first and second group of the amplifiers in the signal path corresponding to said frequency range.
The preferred embodiments of the invention are described in the dependent claims.
In contrast to the prior art, by the solution according to the invention it is possible to implement the selection of signals of the desired frequency range without the switches 51 and 52 (FIG. 2). Because of this, a method and a radio communication device according to the invention achieves higher signal levels compared to the prior art. Due to the achieved higher signal levels, less current is needed to achieve the same transmission power, which is seen as reduced current consumption of the radio communication device. Due to reduced losses, sensitivity on the reception side 11 becomes better.
In addition, a method and a radio communication device according to the invention simplifies the selection of the frequency range, which makes the structure of the radio communication device simpler and reduces the manufacturing costs.